Key-pad and method of producing the same

ABSTRACT

The object of the invention is to find a new configuration, a material, and a manufacturing method of an elastomer keypad provided with a pressing element capable of pressing a switch element with less keystroke loss and clear clicking feeling, and further capable of simplifying processes more than insert molding method which uses the conventional pressing element made of a resin (resin chip). Concave portions  71  and  72  for forming silicone resin pressing elements  41  and  42  which are attached to keypads  2  and  21  are provided at predetermined positions in dies  51, 52, 61 , and  62  for manufacturing a keypad; the concave portions are filled with a silicone resin  9  to start hardening; and subsequently the dies are supplied with a silicone rubber material to form keypad main bodies  2  and  21 , so that keypads  2  and  21  are obtained with the silicone resin pressing elements  41  and  42  being integrated.

The present invention relates to a configuration, a material, and amanufacturing method of a keypad provided with pressing elements whichconstitutes a key unit for mobile equipment such as portable phones andpersonal digital assistants (PDA).

A key unit is one type of components constituting mobile equipment, anda multiplicity of keys (push buttons) for switch operation are assembledand arrayed on a surface of one sheet. FIG. 1 is a perspective view ofone example of such key unit 4 viewed diagonally from the above. Aportion seen as a somewhat large circular shape in the upper right ofthe drawing is a key assembly called multi-direction key, etc., which isintegrally formed from keys for operating switches at five sections(directions) in total of usually four sections in a peripheral ring-likeportion and one section in a central small disk-like portion. The keysarranged in three rows in the left hand direction are called Ten Keys,each of which functions to operate one switch.

Each key comprises a keypad made of a piece of soft elastomer (e.g.,silicone rubber), and a key top made of a piece of hard material (e.g.,polycarbonate resin, hereinafter referred to as “PC resin”) attached onthe surface of the keypad. On the back of the keypad which is not shownin FIG. 1, one or a plurality of switch-pressing projections (what iscalled “pressing elements 3”) are provided at a position on a centerline or at a required position off the center line of each key top. Suchplurality of keys are arrayed on one surface to constitute one key unit4. When a circuit substrate provided with switch elements at positionscorresponding to the pressing elements 3 of each key is attached closeto the bottom surface of the key unit, a series of groups of keyswitches are formed.

In the conventional key units, a pressing element is formed integrallyof the same material as the keypad. In a key for a certain purpose(e.g., a multi-direction key, etc.), however, shortcomings includingoccurrence of keystroke loss or vague clicking feeling at the time ofkey-pressing due to the elastic deformation of the pressing elementshave been pointed out.

Thus, for such specific keys, a method has been conceived of for formingonly a pressing element of a hard resin (e.g., PC resin) separately froma keypad (hereinafter the hard resin is referred to as “resin chip 5”),and, by means of an insert molding method to be carried out by settingin advance the resin chip into a die for keypad-molding, implanting thepressing elements at a predetermined position of the keypad. For such akeypad configuration and a manufacturing method thereof, the applicantof the present application has previously filed a patent application(refer to Patent Literature 1). Patent Literature 1: Japanese UnexaminedPatent Publication No. 2002-279860

In FIGS. 2 and 3, two examples of a multi-direction key with a resinchip implanted in a keypad are shown, which are manufactured accordingto the method of Patent Literature 1. FIG. 2 shows a four-direction keywith a confirmation key which operates five dome-like switches in totalof one central and four peripheral switches with one key top. Aninverted conical-trapezoid-shaped object having a projection at its tipseen in the center of the drawing is a resin chip 5. FIG. 3 also shows afour-direction key with a confirmation key, wherein in order to reducethe thickness of the key, a key top and a keypad are both formed thinly,and the shape of the resin chip is made to be a disk. In this case, thearea of adhesion between the keypad and the resin chip is small, causinga problem in adhesive strength.

In addition to the above-mentioned problem, the keypad configuration andthe manufacturing method thereof disclosed in Patent Literature 1 hasthe steps of: forming a resin chip; carrying out annealing and primertreatments before placing the resin chip in a die in order to securelyadhere a silicone rubber to the resin chip; and setting the resin chipin the die one by one; and the like. Therefore, increase in the numberof steps has been inevitable compared with such method for integrating akeypad with a pressing element with a silicone rubber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the overall configuration of thekey unit including the multi-direction key.

FIG. 2 is a sectional view showing one example of the multi-directionkey with a resin chip implanted by means of an insert molding method.

FIG. 3 is a sectional view showing another example of themulti-direction key with a resin chip implanted by means of an insertmolding method.

FIG. 4 shows sectional views showing the structure of the die providedwith concave portions for carrying out the insert molding method inEmbodiment 1.

FIG. 5 is a sectional view showing the multi-direction key manufacturedusing the die in FIG. 4.

FIG. 6 shows sectional views showing the structure of the die providedwith concave portions for carrying out the insert molding method inEmbodiment 2.

FIG. 7 is a sectional view showing the multi-direction key manufacturedusing the die in FIG. 6.

DISCLOSURE OF THE INVENTION

An object of the invention is to find a new configuration, a material,and a manufacturing method of an elastomer keypad 2 provided with apressing element 3 capable of pressing a switch element with lesskeystroke loss and clear clicking feeling, and, further, capable ofsimplifying processes more than in an insert molding method which usesthe conventional resin chip.

The above-mentioned objects will be achieved by an elastomer keypadformed with a liquid thermosetting resin and provided with a pressingelement for pressing a switch element, and a manufacturing methodthereof.

For a liquid thermosetting resin to be adopted in the invention, ageneral thermosetting resin such as an epoxy resin or a phenol resin, ora silicone resin which is polyorganosiloxane containing in a molecule atrifunctional (unit T) or tetrafunctional (unit Q) siloxane unit wouldbe appropriate. In the silicone resin, particularly a methylphenyl basedstraight silicone resin containing in a molecule a methyl group and aphenyl group, or various types of silicone modified organic resins(e.g., silicone modified epoxy resin) can be used.

Further, for an elastomer constituting a keypad main body, although aline of material varies depending on cases of employing a silicone resinor employing other thermosetting resins as a liquid thermosetting resin,it is preferable to employ a silicone rubber for the former, and toemploy various thermoplastic elastomers (TPE) such as of polyesterbased, urethane based, and polyamide based, for the latter.

In the case of forming a main body of the keypad 2 with a siliconerubber and the pressing element 3 with a silicone resin, a catalyst isto be added onto a concave portion for forming the pressing element in akeypad-molding die (in a one-pack type), or a silicone resin mixed withliquid A and liquid B together with a catalyst is dropped onto theconcave portion (in a two-pack type), and by heating the same to apredetermined temperature, a crosslink-hardening reaction is progressed,so that the silicone resin starts hardening, which leads to theformation of a silicone resin pressing element in the keypad-moldingdie, the pressing element becoming an insertion as it is in the insertmolding method. Subsequently, when the silicone resin of the pressingelement is in a semi-hardened state, a silicone rubber is supplied tothe keypad-molding die, and molding is carried out by means of acompression molding method or a liquid injection molding method (LIM).

Moreover, in the case of forming the keypad main body with athermoplastic elastomer and the pressing element with a thermosettingresin, a thermosetting resin is dropped onto a concave portion forforming a pressing element in a keypad-molding die, and by heating thesame to a predetermined temperature, the thermosetting resin startshardening, which leads to the formation of a thermosetting resinpressing element in the keypad-molding die, the pressing elementbecoming an insertion as it is in the insert molding method.Subsequently, when the thermosetting resin of the pressing element is ina semi-hardened state, by injecting the thermoplastic elastomer, akeypad is integrally formed with the keypad main body with the pressingelement. It should be noted that, in this case, it is possible to formnot only a pressing element but a key top simultaneously by means of atwo-color molding method, for example.

(1) While the method described in Patent Literature 1 requires a resinchip molding process which is entirely different from the keypad moldingprocess, the method according to the invention is directed to forming ofthe pressing element made of a liquid thermosetting resin and the keypadmain body using the same die. Therefore, the method according to theinvention is far more efficient.

(2) While the method according to Patent Literature 1 requires themolded resin chips to be set one by one in the die, the method accordingto the invention only requires the thermosetting resin to be droppedonto the concave portion in the die, which also realizes automationeasily.

(3) In the case of forming the keypad main body with a silicone rubberusing a silicone resin as the liquid thermosetting resin, due tosiloxane bonding which is common to both of them, the bonding betweenthe silicone resin pressing element and the silicone rubber is quiteexcellent, so that no special primer treatment or the like is required.

That allows a keypad manufacturing process to be considerablysimplified.

(4) Further, since the silicone resin pressing element is softer thanthe PC resin pressing element and has moderate elasticity. Therefore,the clicking feeling thereof is softer than that of the PC resin, andfurther the silicone resin pressing element has the same clear clickingfeeling.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the best mode for carrying out the invention will bedescribed by way of two embodiments.

Embodiment 1

FIGS. 4 and 5 show Embodiment 1 wherein a silicone resin and a siliconerubber are used, respectively, as a liquid thermosetting resin forforming a pressing element and as an elastomer for forming a keypad mainbody.

FIG. 4 shows sectional views of the configurations of dies 51 and 52,for manufacturing the four-direction key with a confirmation key shownin FIG. 2 according to the method of the invention. On the surfacefacing a cavity 53 of a lower die 52, a concave portion 71 for forming asilicone resin pressing element is provided, and a mixture of liquids Aand B of silicone resin 9 is dropped onto the concave portion 71 from aninjector 8.

As the silicone resin, a methylphenyl silicone resin which belongs to astraight silicone resin was used. The liquid A and liquid B were mixedat a ratio of 1:1. After deaeration, the mixture was dropped onto a bowl71 from the injector 8 and left to stand for about 30 seconds. Asilicone rubber substrate was placed on the surface of the die cavity 53as the silicone resin started hardening, with the dies 51 and 52 beingclosed, and primary vulcanization was carried out at 170° C. for about 3minutes, followed by secondary vulcanization at 200° C. for about onehour. It should be noted that while in the present embodiment,compression molding method using a silicone rubber substrate was used,it is also possible to employ what is called liquid injection molding(LIM) for injecting a liquid silicone rubber into the die.

FIG. 5 is a sectional view of a four-direction key with a confirmationkey which is manufactured using the dies 51 and 52 in FIG. 4. While theconfiguration in which a key top 1 made of a hard resin is placed on akeypad 2 made of a silicone rubber having an integrally formed pressingelement 3 is the same as that of FIG. 2, a silicone resin pressingelement 41 is provided instead of the resin chip. The pressing element41 is shaped like an inverted conical trapezoid having a rounded tip,with its top surface adhering to the back of the keypad 2. The resinchip in FIG. 2 is modified in such a manner that a silicone rubber layerbe sandwiched between the top surface of the pressing element 41 and thekey top 1 made of a hard resin, in order to improve the brittleness ofthe tip of the resin chip and the clicking feeling.

Embodiment 2

FIGS. 6 and 7 show Embodiment 2 in which, similarly to the aboveEmbodiment 1, a silicone resin is used as a liquid thermosetting resinfor forming a pressing element and a silicone rubber is used as anelastomer for forming a keypad main body.

FIG. 6 shows sectional views of the configurations of the dies 61 and62, for manufacturing a four-direction key with a confirmation key asshown in FIG. 3 according to the method of the invention. On the surfacefacing a cavity 63 of a lower die 62, a concave portion 72 for forming asilicone resin pressing element is provided, and a mixture of liquids Aand B 9 of a silicone resin is dropped onto the concave portion 72 froman injector 8. The types and the handling method of a silicone resin arethe same as those in Embodiment 1.

FIG. 7 is a sectional view of a four-direction key with a confirmationkey which is manufactured using the dies 61 and 62 in FIG. 6. While theconfiguration in which a key top 11 made of a hard resin is placed on akeypad 21 made of a silicone rubber having an integrally formed pressingelement 3 is the same as that of FIG. 3, a silicone resin pressingelement 42 is provided instead of the resin chip. The top surface of thepressing element 42 is configured to adhere to the back of the keypad21, in order to improve the clicking feeling and enlarge the area ofadhesion.

The result of adhesion/peel strength evaluation test of the siliconeresin and the silicone rubber in the keypad 2 made of the siliconerubber described in Embodiment 1 will be given below.

(1) When force applied to the adherend (without primer treatment) of thesilicone resin and the silicone rubber after the primary vulcanizationwas 2.482 kgf in the first sample and was 2.549 kgf in the secondsample, peeling was occurred on the surface of resin/rubber adhesion.The degree of peeling at this time was, respectively, 25% and 30%. Whenthe adhesive strength of the surface of resin/rubber adhesion in thefirst and second samples are calculated from these results, thecalculated adhesive strength are, respectively, 1.92 N/cm² and 1.97N/cm².

(2) When force applied to the adherend (without primer treatment) of thesilicone resin and the silicone rubber after the secondary vulcanizationwas 2.270 kgf in the first sample and was 2.158 kgf in the secondsample, rupture was occurred at the rubber portion. When the adhesivestrength of the surface of resin/rubber adhesion in the first and secondsamples are calculated from these results, the calculated adhesivestrength are, respectively, 1.75 N/cm² and 1.67 N/cm².

(3) For comparison, when force applied to the conventional adherend(with primer treatment) of a chip made of a PC resin and a siliconerubber was 2.397 kgf in the first sample and was 1.954 kgf in the secondsample, rupture was occurred at the rubber portion. When the adhesivestrength of the surface of resin/rubber adhesion in the first and secondsamples are calculated from these results, the calculated adhesivestrength are, respectively, 1.27 N/cm² and 1.03 N/cm².

As can be seen from the above, the adherend (without primer treatment)of the silicone resin and the silicone rubber after the secondaryvulcanization exhibits better adhesive strength than that of theconventional adherend (with primer treatment) of the chip made of the PCresin and the silicone rubber.

INDUSTRIAL APPLICABILITY

The invention relates to mobile equipment such as portable phones,personal digital assistants (PDA), or the like which occupy asignificant position in the information industry and the communicationequipment manufacturer, and more particularly, an improvedconfiguration, a material, and a manufacturing method of a keypadprovided with a pressing element which constitutes a key unit for mobileequipment, so that the invention can contribute to development of theseindustries.

1-3. (canceled)
 4. A keypad made of a soft elastomer such as a siliconerubber, a thermoplastic elastomer and the like comprising a main body ofa sheet form and a plurality of pressing elements to press switchingelements provided on said main body, wherein all or a part of saidpressing elements are formed with a liquid thermosetting resin.
 5. Thekeypad according to claim 4, wherein the liquid thermosetting resin iseither a methylphenyl silicone resin or a silicone modified epoxy resin,and the elastomer is a silicone rubber.
 6. A manufacturing method of akeypad made of a soft elastomer such as a silicone rubber, athermoplastic elastomer and the like comprising a main body of a sheetform and a plurality of pressing elements to press switching elementsprovided on said main body, in which all or a part of said pressingelements are formed with a liquid thermosetting resin, wherein after theliquid thermosetting resin is filled in a concave portion for formingthe pressing element in a keypad-molding die and then starts hardening,the main body of the keypad is formed by providing the elastomer intosaid die.